In the last three decades, civil conflicts have become more complex and intractable than in the past. One reason for this development is the proliferation of rebel groups within the armed oppositions involved in these conflicts. Today, armed oppositions are more likely to be movements composed of loosely connected or competing rebel groups rather than unitary blocs. Yet, despite their centrality to the dynamics of conflict, different structural characteristics of and competitive and power relations within armed oppositions have not been taken in adequate account as possible predictors of civil conflict outcomes. To further our knowledge and cover this gap in the scholarship, the dissertation investigates how and to what extent the fragmentation, internal competition, and internal power distribution of armed oppositions affect civil conflict termination. The dissertation develops a theory that sees the fragmentation of, a moderate and severe competition, and a dispersed distribution of power within armed oppositions as having an impact on the fighting effectiveness of the rebels, the countereffort of the government, bargaining problems, and the intensity of the conflict. This impact shapes, in turn, how civil conflicts end. This theory is tested with a nested analysis consisting of a large-N and a small-N analysis. Through the large-N analysis, the dissertation demonstrates that, at a general level, these characteristics of armed oppositions indeed affect how civil conflicts end. Through the small-N analysis, the dissertation further illustrates the causal mechanisms linking these characteristics to specific civil conflict outcomes. With these findings, the dissertation makes two important contributions. First, it provides generalisable conclusions that remedy the limited generalisability of the scholarship on the phenomena under study. Second, it provides indications on how to resolve conflicts in which the involved oppositions are fragmented and bedevilled by internal competition, thus helping disentangle the proverbial complexity of multi-party civil conflicts.